The impact of conjunctive use of canal and tube well water in Lagar irrigated area, Pakistan

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Abstract

Introduction of the large gravity irrigation system in the Indus Basin in the late 19th century without a drainage system resulted in a rising water table, which resulted in water logging and salinity problems over large areas. In order to cope with the salinity and water logging problem, the Pakistan government initiated installation of 10,000 tube wells in different areas. This not only resulted in the lowering of water table, but also supplemented irrigation. Resulting benefits from the irrigation opportunities motivated framers to install private tube wells. The Punjab area meets 40% of its irrigation needs from groundwater abstraction. Today, farmers apply both surface water flows and groundwater from tube wells, creating a pattern of private and public water control. Sustainable use of groundwater needs proper quantification of the resource and information on processes involved in its recharge and discharge. The field work in the Lagar irrigated area, discussed in this paper, show that within the general picture of conjunctive use of canal water and groundwater, there is a clear spatial pattern between upstream and downstream areas, with upstream areas depending much less on groundwater than downstream areas. The irrigation context in the study area proves to be highly complex, with water users having differential access to canal and tube well water, resulting in different responses of farmers with their irrigation strategies, which in turn affect the salinity and water balances on the fields.

Highlights

► Introduction of irrigation system in the Punjab caused high groundwater tables. ► To cope with salinity and water logging, tube wells were introduced in the 1960s. ► These tube wells meet 40% of the irrigation needs, creating conjunctive use. ► Upstream areas depend less on groundwater than downstream areas. ► This affects salinity and water balances on the fields.

Introduction

Many studies show that irrigation systems are not used by water users as designers had intended in their design (see for example Ahmad et al., 2009, Latif, 2007, Kumar et al., 2010, Zardari and Cordery, 2009, De Veer et al., 1993). Where system management has not been able or willing to deal with interventions by water users, they have occurred nevertheless, with the result that the dichotomy between official rules and actual operation is growing (Facon, 2008). High numbers of farmers worldwide have installed tube wells, recycle drainage water and/or have constructed their own farm reservoirs (Plusquellec, 2002). In this paper we focus on one of the most important global strategies, exploiting groundwater in addition to available surface water flows through canals. Use of groundwater for irrigation gained momentum in the middle of 20th century due to technological developments in drilling and pumping equipments. Currently about one third of the world’s irrigated land mass has groundwater being its source of irrigation. Total groundwater abstraction worldwide is estimated to range between 600 and 700 billion m3 per year (Zektser and Everett, 2004). Almost 300 billion m3 per year of groundwater is used for agriculture in India, China, Nepal, Bangladesh and Pakistan, nearly half of the total world’s annual use. In India groundwater serves about 60% of the total irrigated area. In China provinces of Beijing, Hebei, Henan and Shandong groundwater supplies 65%, 70%, 50% and 50% agricultural water requirements respectively from 3.3 million tube wells. The Punjab, the main food producing province of Pakistan meets 40% of its irrigation needs from groundwater abstraction (Shah et al., 2003).

Today, Pakistani farmers apply both surface water flows from canals and groundwater from tube wells, creating a mixed pattern of public and private water distribution and control (Malik and Strosser, 1993, Qureshi et al., 2010a, Qureshi et al., 2010b). Effects on the water table are clearly noticeable: they generally dropped significantly in the last years in most of the canal commands in Punjab and Sindh provinces (Fig. 1). There seems to be a trade-off between the farmer’s advantage of being able to use water when needed and overexploitation of the groundwater source. From a point of view of conserving water resources, groundwater irrigation may not even be the most favorable type of irrigation. Clearly, however, many farmers do prefer groundwater, among other reasons for the flexibility it allows in their irrigation strategy. As groundwater is accessible for many farmers and does not always require collective action, less capital and planning is required for a scheme development compared to large gravity irrigation schemes. “The development of groundwater has given farmers a great level of control over their crop calendar. They do not have to wait for the availability of canal water, and they can plant their crop at the time that seems best according to their own situation.” (Plusquellec, 2002). Groundwater irrigation is flexible for farmers. However, overexploitation of groundwater is becoming a reality, with in many irrigated areas around the globe groundwater being depleted at undesirable rates.

The Indus Basin Irrigation System of Pakistan is one of the largest contiguous irrigation systems in the world, with its reservoirs, barrages and main canals serving an area of 16 million hectares with some 172 billion m3 of river water per year (Fig. 2) (Aslam and Prathapar, 2006). Introduction of this large gravity irrigation system in the late 19th and early 20th centuries without a drainage system resulted in rising groundwater tables, with associated water logging and salinity problems over large areas. In order to cope with these problems, the Salinity Control and Reclamation Project (SCARP) was started in 1960. Initially 10,000 tube wells were installed, which not only resulted in the lowering of water table, but also supplemented irrigation. Resulting benefits from the full irrigation motivated farmers to install private tube wells. Nowadays, up to 80% of irrigation water needs are provided through tube wells. The irrigation landscape of Pakistan shows this change: tube wells are everywhere, and the density is growing (Fig. 3). The existing irrigation system, with its canal infrastructure and management based on cropping intensities of maximally 50% (one crop during one of the two seasons), has been modified into a system able to support cropping intensities of 200%. Sometimes, additional structures are placed to allow water to flow to the fields to be irrigated.

The large scale picture of groundwater use in Pakistan and its associated problems with groundwater tables and water quality is clear (Qureshi et al., 2010a, Qureshi et al., 2010b, Kijne, 1996). Less clarity exists on the use of groundwater and canal water within irrigated areas. It is well known, however, that several large-scale irrigation systems in Pakistan do show unequal distribution of water use and associated benefits (for example Kumar et al., 2010, Latif, 2007). Differential access to canal water may very well lead to differential use of tube wells. In order to study these relations between (1) farmer position along the canals, (2) water use by canals and/or tube wells and (3) effects on the water balances and groundwater levels, a field research was conducted in the seasons of 2008–2009 and 2009–2010 in the Lagar irrigated area, in the Rechna Doab, Punjab, Indus Basin, Pakistan. In this paper, we discuss results from the 2008–2009 field campaign. We will show that within the general picture of conjunctive use of canal water and groundwater by farmers, there is indeed a clear spatial pattern between upstream and downstream areas. In our study area, farmers in areas upstream along the canal appear to have better access to canal water and hence do not use groundwater as heavily as farmers in downstream areas. These differential accesses are expresses in the water balances in the study area, as well as in salinity profiles in the watercourse. We will also discuss that the water balances and salinity profiles found are the result of farmer responses to the water delivery options available to them. The resulting situation therefore is a conglomerate, an articulation of different processes and actions – natural and human. If this finding holds for more irrigated areas within Pakistan, it may well be that the effects of irrigation on the water system – declining water tables, salinity and pesticide distribution – and the associated costs and benefits of irrigation in general and groundwater use in particular are not equally spread. This may hamper finding general solutions of relevance to all farmers in order to manage Pakistan’s groundwater sources.

Before we move to the Lagar irrigated area and discuss the setup of the field research and its results, we start with an overview of water balance studies of the Indus basin in general and the Rechna Doab area in particular. These studies show to what extent the water sources are (over)exploited. At the end of the paper, in the discussion section, we discuss how our findings are of relevance to the general debate on groundwater sustainability in Pakistan.

Section snippets

Water balances in the Indus basin and Rechna Doab

Water balance of the whole Indus basins (116.2 million hectare) extended in Pakistan (53%), India (33%), China (8%) and Afghanistan (6%) was calculated by Cheema et al. (in preparation) using satellite information and secondary data (Table 1), which shows groundwater depletion. Pakistan’s Indus plain guarantee’s food security of the country through irrigation network originating from the river Indus and its tributaries. Following review of the water balance includes only irrigated part of the

The field work in Lagar Distributary

Constructed over a century ago, Lagar Distributary is a canal diverting water on the right bank of the Upper Gugera Branch canal of the Lower Chenab Canal (LCC) system (Fig. 5). Lagar Canal has a total length of 18,950 m and a design discharge of 1.08 m3/s (38 cubic feet per second or cusecs). Lagar Canal is one of the seven distributaries in the Farooqbad sub division, Upper Gugera Division, Lower Chenab Canal system. Lagar Canal supplies 35 outlets, serving a cultivable command area (CCA) – or

Results

Table 5, Table 6, Table 7 provide an overview of the cropping intensities and the irrigation turns and amounts applied to the crops in the study area. Table 5 shows that the cropping intensities along the Lagar Canal do not differ from upstream to downstream. The results even suggest that in the canal head, the rice crop intensity may be lower, but as the measurement was done in one season and the percentage may well fall within the uncertainty boundary of the measurement itself, no conclusive

Discussion and conclusion

The figures and graphs discussed in this paper show that differential patterns of water use – from different sources – and salinity are found in irrigation units in the Lagar area in Rechna Doab. Underneath these data is another reality that is highly relevant to introduce: the human response within this highly complex irrigation context. Farmer strategies are an important element in the process of water flows and salinity. For example, the samples fields at the head and middle of the head

Acknowledgements

This research could not have been conducted without the strong support of the Nuclear Institute for Agriculture and Biology (NIAB), Faisalabad, Pakistan. In analyzing the large number of soil samples to determine the EC values, the support of Muhammad Kamran, Lab. Assistant, is kindly acknowledged.

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